52 



DECOMPOSITION OF SULPHATES BY HEAT. 



posed by heat by heat, by passing it through an incandescent porcelaim 

 ilone. tube, thus obtaining oxigen and sulphurous acid gas. 



This experiment explains the decomposition of sulphates. 



Ditfirent ef» " "^'^ *^^ neutral or acid sulphates, that lose their acid at 



fccts of heat a temperature below that required for decomposing sul- 



onsupiates. ph^rjc acid, will decompose without giving out oxigen or 



sulphurous acid. Those, on the contrary, that retain all 



their acid so strongly as to resist a heat equal or superior to 



that which decomposes sulphuric acid, will give out only 



oxigen gas and sulphurous acid. Lastly, as a compound 



does not equally retain every portion of its elements, there 



are sulphates, the decomposition of which will partake of 



the two preceding, and which will give out sulphuric acid, 



oxigen gas, and sulphurous acid." 



Thus then, setting aside the particular influence of a 

 given base, we should consider the affinity, that unites the 

 sulphuric acid to the base with which it forms a sulphate, as 

 a force that enables it to support without being volatilized a 

 heat sufficient to decompose it ; while, if it had been free, 

 it would have withdrawn itself from the action of the heat, 

 long before it experienced the degree necessary for this de- 

 composition. But this force of affinity is likewise an addi- 

 tional obstacle to be overcome by the action of heat : and 

 this obstacle is very considerable, when the base undergoes 

 no alteration by heat, as the oxide in the sulphate of lead, 

 and the fixed alkalis in their sulphates. 



The paper contains many other very delicate researches of 

 considerable importance to the chemical theory of several 

 phenomena, but I shall here finish my abstract with the 

 following 



r'Jccts of the 

 attraction of 

 the base for 

 I he acid. 



<ieneral de- 

 ductions. 



Decomposi- 

 tion of the me- 

 tallic sul- 

 phates. 



*' Conclusion. 



*' 1st. All the metallic sulphates are decomposable by 

 the action of heat, affording results that depend on the af- 

 finity of the metals for sulphuric acid. The sulphates in 

 which the acid is but little condensed yield only sulphuric 

 acid by distillation. Those that retain it more strongly, and 

 are ^insoluble, give out sulphurous acid and oxigen gas. 

 Lastly, those that have properties common to both- the 



precedino- 



